1. Field of the Invention
The invention relates to image processing apparatus and method for efficiently compressing an image and to a storing medium in which such a method has been stored.
2. Related Background Art
In recent years, computers and networks have remarkably been developed and various information such as character data, image data, audio data, and the like are handled in a computer and in a network.
With respect to the image data and audio data, data of a relatively large data amount is often handled. Therefore, a process to reduce the data amount by compressing the image data and audio data has been performed hitherto.
For example, by compressing the image data, a large quantity of image information can be transmitted through a network at a high speed.
According to the above image compressing technique, a system (generally called a JPEG) for compressing a multivalue still image in the ITU-T Recommendation T.81 is known and a system (generally called a JBIG) for compressing a binary still image in the ITU-T Recommendation T.82 is known.
The JPEG system is suitable for compression of a natural image such as a photograph. The JBIG system is suitable for compression of a binary image such as a black and white character.
According to the conventional JPEG system and JBIG system, all images of multivalue images (photograph or the like) and binary images (character image, diagram image, or the like) cannot be efficiently compressed without deteriorating a picture quality.
To solve the above problem, a method of separating a multivalue image portion and a binary image portion in one picture plane and compressing them by different compressing systems is also known.
The JPEG system is suitable for encoding in a case where natures of images locally differ. By properly switching an encoding system every area in each block, an efficient encoding can be executed while suppressing a deterioration of the picture quality. According to the above system, after multivalue image data was converted into a frequency component every block, by entropy encoding the frequency component, even if the natures of the images locally differ, the encoding according to each block can be executed.
On the other hand, the JBIG system does not execute the encoding on a block unit basis.
However, the system for compressing the multivalue image and binary image as mentioned above does not satisfy all of the requirements of the user yet. Therefore, a new image compressing system is proposed to further improve a picture quality, a processing speed, or an encoding efficiency.
The invention is made in consideration of the above conventional systems and it is a main object of the invention to provide a new system which can efficiently compress and can keep a high picture quality for any one of a multivalue image and a binary image.
Particularly, another object of the invention is to provide an encoding system of a high compression ratio in an encoding system for encoding an image every block.
To accomplish the above objects, according to one preferred embodiment of the invention, there is provided an image processing apparatus comprising:
first converting means for generating conversion coefficients of M values by converting input image data by a first system;
second converting means for generating conversion coefficients of N values (M greater than N) by converting the input image data by a second system;
input means for selectively inputting the conversion coefficients of M values or the conversion coefficients of N values; and
output means for outputting first information indicating a position where a significant conversion coefficient exists in a block constructed by either ones of the conversion coefficients inputted by the input means and second information indicating the significant conversion coefficient.
According to the invention, still another object of the invention is to efficiently entropy encoding block division information which is generated by a block division processing as an element technique of the new image encoding system.
To accomplish the above object, according to one preferred embodiment of the invention, there is provided an image processing apparatus comprising:
output means for outputting division information indicating whether each of a plurality of blocks including an encoding subject block has further been divided into a plurality of blocks or not; and
entropy encoding means for entropy encoding the division information corresponding to the encoding subject block on the basis of a presumption probability according to a division situation of a neighboring block of the encoding subject block.
The above and other objects and features of the present invention will become apparent from the following detailed description and the appended claims with reference to the accompanying drawings.